1. Field of the Invention
The present invention relates to an eye refractive power measurement apparatus for measuring eye refractive power of an eye of an examinee objectively.
2. Description of Related Art
Conventionally, there is known an eye refractive power measurement apparatus which projects spot-shaped measurement light onto a fundus via a central pupillary portion and photo-receives reflection light from the fundus via a peripheral pupillary portion and a ring-shaped aperture (opening) which is arranged at an optically conjugate position with a pupil using a two-dimensional photodetector or the like to obtain eye refractive power based on a photo-receiving result thereof (see Japanese Patent Application Unexamined Publication No. Hei11-225963). In such an apparatus, in order to ensure measurement accuracy, the size of the ring-shaped aperture is set so as to photo-receive the reflection light from the fundus via a ring-shaped region of 2 mm in inside diameter and 3 mm in outside diameter on a pupillary surface.
However, some of the aged people and the like have a pupil which is not more than 2 mm in diameter, and there is a case where measurement cannot be performed with a constitution that the measurement light from the fundus is photo-received via the ring-shaped region of 2 mm in inside diameter and 3 mm in outside diameter on the pupillary surface. In order to cope with this problem, it is conceivable that the ring-shaped region on the pupillary surface is made smaller to be 1.4 mm in inside diameter and 2.4 mm in outside diameter (i.e., the size of the ring-shaped aperture is made smaller). However, in this case, corneal reflection or crystalline lens reflection of the projected measurement light tends to become noise, and for a normal eye with a large enough pupil diameter, measurement accuracy is sometimes contrarily lowered.